1. Field of the Invention
The present invention relates to instruments for sound reproduction, and more particularly, to low frequency loudspeaker drivers, conventionally referred to as Woofers.
2. Discussion of the Prior Art
A great variety of moving coil loudspeaker designs have been proposed for high quality low frequency sound reproduction, and many have gone into commercial use. These are typically included in a modern full range loudspeaker system utilizing different speakers for different segments of the sound spectrum. For example, a xe2x80x9cwooferxe2x80x9d is used for bass or low frequencies, a xe2x80x9cmid-rangexe2x80x9d is used for intermediate frequencies and a xe2x80x9ctweeterxe2x80x9d is used for the highest frequencies in the reproduced spectrum.
It is generally accepted that loudspeakers with sufficient size to produce adequate bass have well understood limitations. In particular, break-up of the cone motion into standing waves, beaming and other directional effects cause poor sound reproduction when driven by more challenging audio signals.
Typical prior art woofers utilize frustoconical baskets supporting frustoconical driver diaphragms, each having a circular peripheral edge. Customarily, the circular small end of the frustoconical diaphragm supports an axially aligned cylindrical voice coil former which carries a conductive voice coil having positive and negative terminal ends. Conventional woofers utilize baskets which closely follow the frustoconical shape of the driver diaphragm and support an axially aligned motor magnet and the circular diaphragm surround in a co-axial alignment, permitting the axial oscillating movement of the diaphragm in response to excitation of the voice coil.
In some high-end automotive or xe2x80x9ctwelve voltxe2x80x9d applications, music aficionados and auto-sound competitors will install several woofers in a two-dimensional array on a baffle or enclosure surface; for example, it may be desirable to install five woofers in two rows, with a row having two woofers juxtaposed with a second row having three woofers. When installers attempt to install as many conventional woofers as possible in a baffle, there are, necessarily, three-point star-shaped baffle surface spaces left uncovered between the adjoining woofer baskets. The ideal installation, from an afficionado""s or competitor""s viewpoint, is one having the entire baffle covered with woofer diaphragms. The uncovered baffle spaces leave the consumer with the impression of wasted space.
Another concern for music afficionados and auto-sound competitors is woofer failure due to thermal or mechanical overloading problems. Substantial amounts of power are required to provide competition-winning sound pressure levels, often well over 150 decibels (dB). Signals having such power require very large current flow through voice coil conductors, thus generating substantial amounts of heat, and drive the woofers to extreme excursions, thus generating extreme mechanical loads on driver diaphragms and suspensions. In order to overcome these perceived difficulties, the inventor has developed a number of new woofer configurations.
Accordingly, it is a primary object of the present invention to overcome the above mentioned difficulties by providing a woofer diaphragm having a polygonal peripheral shape, preferably supported within a basket having a matching polygonal peripheral shape.
Another object of the present invention is to provide a woofer structure having a faceted diaphragm surface with a hexagonal peripheral edge, preferably supported within a basket having a matching hexagonal peripheral shape.
Another object of the present invention is to provide a woofer configuration which permits mounting a plurality of woofers in a two-dimensional planar array having adjoining basket edges which interlock in a pattern that uses substantially all of the baffle surface area.
Yet another object of the present invention is to provide a woofer diaphragm which is free of the traditional standing wave break-up modes associated with traditional frustoconical woofer diaphragm shapes.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
A low frequency loudspeaker driver has polygonal diaphragm surfaces. In a first embodiment of the present invention, the peripheral edge of a loudspeaker driver diaphragm is polygonal (preferably hexagonal or six sided), wherein each of the six peripheral sides are of equal length and meet in rounded or radiused corners. The hexagonal loudspeaker driver is supported within a matching hexagonal cross-section truncated pyramid shaped basket having a hexagonal peripheral mounting flange.
The hexagonal woofer of the first embodiment is adapted to be mounted on a substantially planar baffle in a variety of densely packed arrays such that virtually no wasted baffle space is visible between the driver basket peripheral edges. The faceted hexagonal diaphragm shape provides an increase in effective cone surface area of approximately ten percent as compared to similarly sized conventional frustoconical woofers having circular peripheral edges.
In one embodiment in accordance with the present invention, a nominally 12 inch hexagonal cone has an outer peripheral edge which is substantially hexagonal but includes a faceted, multi planar diaphragm configuration terminating in a substantially circular voice coil support at the back of the cone. This novel configuration includes a polymer or plastic (e.g., Apical(copyright) polymer) voice coil former suspended in an annular gap within the motor structure. The voice coil former supports a long-throw voice coil. The hexagonal driver of the preferred embodiment preferably includes a hexagonal dust cap covering the aperture supporting the voice coil former. The dust cap is comprised of contiguous substantially planarfacets defining six equilateral triangle segments and provides a striking visual effect. Preferably, printed indicia are included on the dust cap to provide the purchaser with an attractive visual presentation.
In an alternative embodiment of the low frequency loudspeaker driver of the present invention, the polygonal configuration of the diaphragm is augmented with rounded or radiused outer segments to provide a circular peripheral edge, thus providing a polygonal faceted diaphragm surface with a circular diaphragm edge. A frustoconical basket having circular inner and peripheral edges supports the circular peripheral edge of a polygonal faceted diaphragm. In an exemplary embodiment, a hexagonal, 6 faceted woofer cone surface supports a hexagonal dust cap. The outer peripheral edge of the diaphragm is circular and a faceted peripheral segment is affixed to an intermediate shoulder having six facets. The intermediate shoulder is terminated at its interior in a polygonal segment which is, in turn, terminated in a small radiused circular opening adapted to support a conventional cylindrical voice coil former. The driver of this embodiment also supports a six facet hexagonal dust cap, preferably bearing a visually striking logo.
Another aspect of the loudspeaker of the present invention is a system of vents arrayed around the spider plateau of the driver motor structure. The vents direct cooling airflow to the voice coil, thereby lowering voice coil temperature during high-power operation. A venting experiment set forth test results from a number of prototypes and the conclusions were used in selecting venting aperture locations. The selected venting aperture configuration comprises six thru holes near the front plate and just under the spider plateau: the six holes are arrayed around the motor sidewall in a circle concentric with the voice coil and are equally spaced. An annular mesh vent screen is aligned with the six holes and filters passing cooling air. The selected venting aperture configuration demonstrated significant voice coil cooling and provided enhanced long-term, high power reliability.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components.